In Perl, what is a good way to perform a replacement on a string using a regular expression and store the value in a different variable, without changing the original?
I usually just copy the string to a new variable then bind it to the s/// regex that does the replacement on the new string, but I was wondering if there is a better way to do this?
$newstring = $oldstring;
$oldstring =~ s/foo/bar/g;
This is the idiom I've always used to get a modified copy of a string without changing the original:
($new = $original) =~ s/foo/bar/;
Just a word of caution, John's answer correctly answers the question, but
($new = $original) =~ s/foo/bar/;
Is equivalent to
$newstring = $oldstring;
$newstring =~ s/foo/bar/g; #Modify $newstring instead of $oldstring
Which is I think what you meant in the first place. Probably better edit the question and correct your sample code.
If you write Perl with use strict;, then you'll find that the one line syntax isn't valid, even when declared.
With:
my ($newstring = $oldstring) =~ s/foo/bar/;
You get:
Can't declare scalar assignment in "my" at script.pl line 7, near ") =~"
Execution of script.pl aborted due to compilation errors.
Instead, the syntax that you have been using, while a line longer, is the syntactically correct way to do it with use strict;. For me, using use strict; is just a habit now. I do it automatically. Everyone should.
#!/usr/bin/env perl -wT use strict; my $oldstring = "foo one foo two foo three"; my $newstring = $oldstring; $newstring =~ s/foo/bar/g; print "$oldstring","\n"; print "$newstring","\n";
Under use strict, say
(my $new = $original) =~ s/foo/bar/;
instead.
The one-liner solution is more useful as a shibboleth than good code; good Perl coders will know it and understand it, but it's much less transparent and readable than the two-line copy-and-modify couplet you're starting with.
In other words, a good way to do this is the way you're already doing it. Unnecessary concision at the cost of readability isn't a win.